1. Field of the Invention
The present invention relates to an apparatus and method for extracting region information of objects queried in object extraction target images (still images or video sequences), from which the object is to be extracted, in which an image of the object to be extracted is given as a query image, the object extraction target image is processed in unit of pixels to determine the position of the object therein, and the query image is compared with an image composed of segmented regions of the object extraction target image at a position determined as the position of the object in terms of color feature, texture feature, and similarity in spatial disposition.
2. Description of the Related Art
Approaches of extracting an object from an image are largely divided into three categories, i.e., motion based extraction using the movement of an object, feature based extraction using the feature of an object region, and a manual operation using video edition software.
Approaches of motion based extraction are divided into extraction of a motion area based on calculation of frame differences, extraction based on background subtraction, and extraction based on motion analysis. In approaches using frame differences disclosed in U.S. Pat. Nos. 5,500,904 and 5,109,435, differences in brightness among consecutive image frames are calculated to extract motion, which is a basic method of extracting a motion area. In an approach based on background subtraction which is disclosed in U.S. Pat. No. 5,748,775, a background image is reconstructed using temporal changes of image feature parameter values, and an object is extracted using a difference between the reconstructed background image and an original image. In an approach based on motion analysis which is disclosed in U.S. Pat. No. 5,862,508, the moving direction and velocity of a moving object are calculated to extract a motion area. This approach is a most general motion area extraction method which can be applied even when illumination conditions or the structure of a background changes. The above-described motion based extraction can be applied when there is the appropriate quantity of motion of an object in consecutive images. However, it is difficult to apply the motion base extraction to still images, images having a slight motion, or images having exceeding motion velocity.
Approaches of feature based extraction can be divided into template matching, multi-value threshold based segmentation, and feature matching. In a template matching method disclosed in U.S. Pat. No. 5,943,442, an object to be extracted is defined as a template image, and a region for which a normalized correlation value is maximum is extracted as an object region in an image to be searched. However, when the size of the object changes or the object rotates, the normalized correlation value sensitively reacts, so extraction performance decreases. In a method of extracting an object using multi-value thresholds which is disclosed in U.S. Pat. No. 5,138,671, the distribution of the lightness values or color values of an image is segmented into a plurality of regions using multi-value thresholds, and each region is considered as an object region. In this method, it is not easy to accurately distinguish an object from a background.
In a manual method using video editing software, an object is manually extracted. According to this method, accuracy of object extraction is high, but an amount of time is required. Accordingly, this method is not proper to editing of database images including successive images or a large amount of images.